Add external audio clocks nodes to RZ/G2L (a.k.a R9A07G044) SoC DTSI.

The external audio clocks are configured as 0 Hz fixed frequency clocks by
default. Boards that provide audio clocks should override them.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20210814135526.15561-2-biju.das.jz@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>